Prevalence of autism spectrum disorders and influence of country of measurement and ethnicity

Background The prevalence of autism spectrum disorders (ASD) is generally somewhat lower in countries outside of North America and Europe. While there are culture-specific patterns of social cognitive processing, the influence of such patterns upon ASD prevalence has yet to be fully explored. Methods A comprehensive literature search for original articles reporting ASD prevalence was undertaken. Data across studies were compared with a particular focus on variables of geographic residence and ethnicity. Results ASD prevalence varies across countries in a manner that appears to suggest that the greatest influence is due to methodological variables. The nature of a potential influence of culture-specific patterns of cognitive processing upon prevalence remains unknown. The available little data concerning the association between ethnicity and prevalence are limited to studies within the United States (US) showing differences in children of Hispanic descent relative to Whites, a finding for which a definitive explanation is lacking. Conclusions Available evidence suggests that methodological factors are largely responsible for differences in ASD prevalence across studies. The much discussed increase in prevalence inASDhas been observed worldwide, suggesting that the refinement of diagnostic methodology and/or broadening diagnostic concept is not limited to Western countries. Within individual countries, only in the US has the influence of ethnicity upon ASD prevalence been examined in depth. In the US, children of Hispanic descent have the lowest prevalence of ASD, while Whites tend to have the highest prevalence of ASD. Hypothesized etiological factors for such prevalence differences include methodological factors, socioeconomic variables, and bias.